Lipo dropped to 2.7V in storage

[Baron]

I just checked one of my lipos - a 4s hardcase pack from hobbyking http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=18631
I have 10 total which have been sitting for about 2 months at a storage charge level. One cell in one of the packs was sitting at 2.72V, with the rest of the cells in that pack around 3.4V. I must have stored this pack at an empty charge by accident. All of the other packs which had been sitting for the same amount of time were at a healthy storage voltage, around 3.7V.

I have put about 50-100 cycles through these batteries on my bike in the last year, and the packs have always been healthy. I don't think that bad cell was overdischarged, so it must have a high internal resistance causing it to discharge in storage? Should that low cell be considered lost or is there a safe way to bring it back to life?

 

[wesnewell]

Charge it and test it. While it may be weak, if it test ok, I'd use it, and have used cells that have gone that low.

 

[DVDRW]

I had new Wina 10ah Lifepo4 cell 0V (3 year storage)
Recovered 90% of its capacity

 

[izeman]

if all other cells in the pack are at the same level, and only one of them is really low, then i would dump that cell. this is the weakest cell. and it will determine the performance of the whole pack. it will charge to 4.2v without any issues for sure, and will work for some time.
you should test the pack's/cell's internal resistance and see how much it changed. with higher resistance this cell is going to be hotter than then others.
charging all cells to a certain level, putting it on a shelf and watching the voltage drop is a known (as well as time consuming) test to determine if a pack is well matched.
this cell for sure is NOT as good as the rest. what will happen: noone knows.

 

[Syonyk]

I had new Wina 10ah Lifepo4 cell 0V (3 year storage)
Recovered 90% of its capacity

LiFePO4 is a rather significantly different chemistry than the common LiCoO2 used in unspecified lipo packs.

 

[Ykick]

You found a "leaker" cell. Leakers self-discharge while sitting and while they can often perform well in regard to IR/C-rate, capacity, etc., the fact they're leaking off voltage should make someone nervous enough to cull them from the herd.

Whenever I buy new RC Lipo I always capacity test, IR test and let 'em sit fully charged for a few days to see if any leak significant voltage off. If they pass those 3 tests, I'm fairly confident using them. If they fail any of those tests, I write a comprehensive description of the test data and request replacement pack.